Method and fluid system for moving subsurface well equipment in well tubing

ABSTRACT

A fluid system for running and retrieving subsurface well equipment in a well tubing by fluid flow through a curved entrance tubing without restricting the length of the well equipment. The curved entrance tubing having an inside diameter greater than the inside diameter of the well tubing for transporting a first larger locomotive which carries a second smaller locomotive for movement in the well tubing in response to fluid flow. Releasable engaging means between the larger and smaller locomotive whereby the larger locomotive may transport the smaller locomotive through the enlarged curved entrance tubing but allow the smaller locomotive to move alone in the smaller well tubing. A retaining nipple between the enlarged curved entrance tubing and the well tubing for retaining the larger locomotive while the smaller locomotive travels in the well tubing whereby the larger locomotive is in position to receive the smaller locomotive upon its return. A retrieving mechanism for retrieving the enlarged locomotive from the retaining nipple.

United States Patent Tausch et a1.

METHOD AND FLUID SYSTEM FOR MOVING SUBSURFACE WELL EQUIPMENT IN WELLTUBING Inventors:

Assignee:

Filed:

Appl. No.1

Gilbert H. Tausch; Fred E. Watkim,

both of Houston, Tex.

Cameo, Incorporated, Houston, Tex.

Dec. 15, 1971 US. Cl. ..166/315, 166/77, 166/156 Int. Cl. ....E2lb23/00, E2lb 23/04, E2lb 43/10 Field of Search ..166/75.70, 77, 153,

References Cited UNITED STATES PATENTS Schramm et al.... Coberly et al.Yetman Primary Examiner-Stephen J. Novosad Attomey-James F. Weiler etal.

[57] ABSTRACT A fluid system for running and retrieving subsurface wellequipment in a well tubing by fluid flow through a curved entrancetubing without restricting the length of the well equipment. The curvedentrance tubing having an inside diameter greater than the insidediameter of the well tubing for transporting a first larger locomotivewhich carries a second smaller locomotive for movement in the welltubing in response to fluid flow. Releasable engaging means between thelarger and smaller locomotive whereby the larger locomotive maytransport the smaller locomotive through the enlarged curved entrancetubing but allow the smaller locomotive to move alone in the smallerwell tubing. A retaining nipple between the enlarged curved entrancetubing and the well tubing for retaining the larger locomotive while thesmaller locomotive travels in the well tubing whereby the largerlocomotive is in position to receive the smaller locomotive upon itsreturn. A retrieving mechanism for retrieving the enlarged locomotivefrom the retaining nipple.

20 Claims, 4 Drawing Figures PAIEmEn P m 3,727. 693

SHEET 2 UF 2 METHOD AND FLUID SYSTEM FOR MOVING SUBSURFACE WELLEQUIPMENT IN WELL TUBING BACKGROUND OF THE INVENTION It is conventionalto run and pull subsurface well equipment from a well tubing and performother subsurface operations by the use of pump-in piston like devicesgenerally referred to as locomotives. The subsurface equipment isfrequently pumped through an entrance loop or curved tubing, aconventional size having a five foot radius. The curved radius of theentrance loop greatly limits the allowable straight length of a givendiameter well tool that may freely pass through the loop since the loopis constructed of pipe that is of the same internal diameter as that ofthe well tubing.

The present invention is directed to providing improvements in a pumpingsystem for moving subsurface well equipment into and out of a welltubing through a curved entrance loop which greatly increases theallowable longitudinal length of a given diameter tool that can passthrough the entrance loop whereby many of the tools, valves and otherequipment previously designed and proven for use with conventionalwireline operations can be used in a pumping system.

SUMMARY The present invention is directed to a pumping system for movingsubsurface well equipment through a curved entrance loop into welltubing by providing the curved entrance tubing with an inside diametergreater than the inside diameter of the well tubing whereby well toolsof greater longitudinal length may pass through the curved entranceloop. However, the locomotives carrying the well equipment mustnecessarily be of suitable dimensions that will allow them to be pumpedthrough the tubing. Therefore, it is another object of the presentinvention to provide a first locomotive having an outside diametersubstantially equal to the inside diameter of the enlarged curvedentrance loop for movement therein.

And since the enlarged entrance tubing or loop will be larger than thewell tubing, the present invention is also directed to providing asecond locomotive which may be releasably connected and disconnectedfrom the first locomotive so that the second locomotive may betransported through the entrance loop by the first locomotive andthereafter be disconnected and pumped through the well tubing fortransporting the well equipment into and out of the well tubing.

A still further object of the present invention is the provision of aretaining nipple between the enlarged curved entrance tubing and thesmaller well tubing that will retain the first larger locomotiveadjacent the lower end of the enlarged curved loop when fluidcirculation is reversed so that the first locomotive is in position toreceive the second smaller locomotive traveling in the well tubing onits return for connection thereto and transporting the smallerlocomotive back through the enlarged curved tubing.

Since there is always the possibility that the smaller locomotivetraveling in the well tubing or its attached well equipment may becomeinoperative or stuck and must be fished out of the well tubing, it is astill further object of the present invention to provide means forretrieving the large first locomotive from the retaining nipple ifnecessary so that fishing or other operations may be performed.

Yet a still further object of the present invention is the method ofrunning subsurface well equipment into a well tubing through an enlargedcurved tubing connected to the upper end of the well tubing byreleasably connecting a first locomotive sized to be transported throughthe enlarged tubing to a second locomotive sized to be transportedthrough the well tubing, pumping the first locomotive through theenlarged tubing carrying the second locomotive and well equipmenttherethrough, releasing the locomotives from each other, retaining thefirst locomotive adjacent the junction between the enlarged tubing andthe well tubing, and pumping the second locomotive in the well tubingthereby carrying the well equipment to the desired location in the welltubing.

The present invention further contemplates the method of retrieving wellequipment from the well tubing after the well equipment is connected tothe second locomotive by pumping the second locomotive and the wellequipment up the well tubing and connecting the second locomotive to thefirst locomotive and thereafter pumping the first locomotive up theenlarged tubing carrying the second locomotive and the well equipment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational schematicdrawing showing one environment in which the present invention may beused, FIG. 2 is an enlarged fragmentary elevational view illustratingthe present invention moving a well tool through a curved loop,

FIG. 3 is an enlarged fragmentary elevational view, in cross section,illustrating the releasable connection between the locomotive and theretaining nipple, and shows the locomotives in position for releasingfrom each other and the connection of the larger locomotive to theretaining nipple, and

FIG. 4 is an enlarged fragmentary elevational view, partly in crosssection, illustrating the enlarged locomotive seated in a retainingnipple and being disengaged therefrom by a retrieving tool.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,and particularly to FIG. 1, an offshore oil/gas platform generallyindicated by the reference numeral 10 is provided to service a wellhaving a tubing 12. It is conventional to run and pull subsurface wellequipment to the tubing 12 from the platform 10 through a curvedentrance loop or tubing 14 which may include one or more curved portions16. This is normally accomplished by pumping equipment down and up thetubing 12 by a pair of hydraulic lines (only one of which is shown) bypiston like devices normally called locomotives. Normally, the radius ofthe curved portion 16 is restricted to a particular radius, for examplefive feet, to reduce space requirements and other problems. However, the5 foot radius restriction greatly limits the longitudinal length of agiven diameter object that may freely pass through the loop 16 as thetubing 14 has been the same internal diameter as that of the well tubing12.

For example, if a well tubing has a 2 inch internal diameter a well toolhaving a one and /2 inch outside diameter can only be 15.52 inches longto pass through a 5 foot radius loop. Obviously, this significantlyreduces the longitudinal length of various well tools from that whichhave been used in the past in conventional wireline operations. However,should the curved portion 14 be constructed of four inch internaldiameter pipe, a 1% inch O.D. well tool 34.64 inches long can passthrough the loop 14.

Therefore, the present invention is directed to providing, as best seenin FIG. 2, a curved entrance tubing or loop 14 having an inside diametergreater than the inside diameter of the well tubing 12 thereby allowingthe passage of well tools, for example only, a gas lift valve carried bya conventional setting tool which may pass through the curved tubing 14.Thus, many of the tools, valves and other equipment which have beenproven and used in conventional wireline operations can be used in thepresent pumping system. Of course, the locomotives must generally be ofsimilar dimensions as the tubing through which they are pumped in orderthat a seal be maintained between the internal diameter of the tubingand the outside diameter of the locomotive for pumping the locomotivesthrough the tubing.

Still referring to FIG. 2, a first locomotive 22 is provided having anoutside diameter substantially equal to the inside diameter of thecurved tubing 14 for move ment therein by conventional pumpingoperations.

A second locomotive 24 is provided having an outside diametersubstantially equal to the inside diameter of the well tubing 12 formovement in the well tubing 12 in response to fluid flow in the welltubing 12. The second locomotive 24 is releasably connected to the firstlocomotive 22 and supports additional conventional equipment such asanother locomotive 25, weight bars 26, knuckle joint 28 and/or othersuitable equipment such as the well tool 20.

The present invention is also directed to providing a method andapparatus for releasably connecting the first locomotive 22 to thesecond locomotive 24 for carrying the well tool through the curvedtubing 14 down to the well tubing 12. Thereafter, the second locomotive24 is disconnected from the first locomotive 22 and may be pumped downthe well tubing 12 as is conventional to perform conventional runningand pulling operations as well as other well services. Thereafter, thesecond locomotive 24 may be pumped uphole through the well tubing 12 andreconnected to the first locomotive 22 and the entire assembly pumped upthrough the curved tubing 14 to the platform 10.

Referring now to FIG. 3, the structure ofa releasable connection betweenthe first locomotive 22 and the second locomotive 24 is best seen. Thefirst locomotive 22 generally includes a body having a sealing means 32thereon sized for being propelled through the tubing 14 by fluidmovement. A locking dog 34 is pivotally connected to the body by a pin36. The second locomotive 24 also includes a body 38 having a sealingmember 40 thereon sized for coaction with the internal diameter of thewell tubing 12 for movement therein in response to fluid flow. Thesecond locomotive 24 includes a groove 42. The first locomotive 22 ispositively latched to the second locomotive 24 by the action ofashoulder 46 of the locking dog 34 coacting with the groove 42 of thesecond locomotive 24. The locking dog 34 is held in the latchingposition by a sliding sleeve 48 yieldably urged against the locking dog34 by a spring 50. Thus, the first locomotive 22 may be pumped throughthe enlarged curved tubing 14 upwardly or downwardly and carries thesecond locomotive 24 and any attached equipment when the locking dog 34is engaged in the groove 42.

Referring to FIGS. 2 and 3, a retaining nipple generally indicated bythe reference numeral 60 is provided between the enlarged curved tubing14 and the Well tubing 12 for retaining the'first locomotive 22 withinthe lowermost portion of the enlarged tubing 14 when fluid circulationtherethrough is reversed so as to keep the first locomotive 22 at thelowermost portion of the tubing 14 so that it is in position to receivethe second locomotive 24 on its return up the well tubing 12 forre-engagement with the first locomotive 22 and transportation backthrough the tubing 14. In addition, the retaining nipple 60 may assistin performing the function of releasing the second locomotive 24 fromthe first locomotive 22 as well equipment is being 'run into the welltubing 14. The retaining nipple 60 may include a first upwardly directedshoulder 62, a recess 64 therebelow, and a second upwardly directedshoulder 66.

As the first locomotive 22 and second locomotive 24 are pumped down thecurved tubing 14 in the well equipment and the second locomotive 24enters the well tubing 12, and as best seen in FIG. 3, shoulder 68 onthe sliding sleeve 48 engages the upwardly directed shoulder 62 of theretaining nipple 60 and prevents further downward movement of the sleeve48. As the locomotives 22 and 24 continue downwardly, the

locking dog 34 is released from the control of sleeve 48 and moves outof the groove 42 on the second locomotive 24 thereby allowing the secondlocomotive 24 and well tool 20 to continue down the well tubing 12.

An outward swing of locking dog 34 is generated by the action of theshoulder 70 on the second locomotive 24 and a second sliding sleeve 72yieldably urged downwardly by a second spring 74 carried by thebody 30of the first locomotive 22. And as best seen in the lower portion ofFIG. 4, the locking dog 34 moves into recess 64 of the retaining nipple60 thereby retaining the first locomotive 22 in the retaining nipple 60in a locked position. The shoulder 76 at the lower end of the sleeve 72engages the locking dog 34 to retain the locking dog 34 in the recess64. Further downward movement of locomotive 22 is prevented as shoulder77 on locomotive 22 contacts shoulder 66 of the retaining nipple 60.

It is to be noted that the first locomotive 22 includes an open borewhich is normally blocked when the second locomotive 24 is connected tothe first locomotive 22, but which is open when the second locomotive 24is released, thereby allowing fluid flow through the first locomotive 22to propel the second locomotive 24 down the well tubing 12. With thefirst locomotive 22 locked in the retaining nipple 60, flow in eitherdirection through the tubing 12 and 14 may be generated without movingthe first locomotive 22 from the retaining nipple 60. Of course,suitable pressure relieving means may be provided to prevent a hydraulicblock between the first locomotive 22 and the second locomotive 24in thelower end of tubing 14 as the second locomotive 24 enters tubing 1.2.Normally, the locomotive seals 32 and 40 will allow passage ofsufficient fluid to prevent such blockage, but a port 17 may be providedin the body 30 of locomotive 22 if desired.

And with the second locomotive 24 released from the first locomotive 22the second locomotive 24 may be moved through the well tubing 12 toconventionally perform the operation of running and pulling subsurfaceequipment as well as performing other subsurface operations.

When it is desired to return the second locomotive 24 to the surface, itis pumped back up to the first locomotive 22 and the nose 80 oflocomotive 24 contacts the lower end 76 of the sleeve 72 oflocomotive 22moving the sleeve 72 against the spring 74 thereby releasing the lockingdog 34 from the recess 64 in the retaining nipple 60. The slidablesleeve 48 is then urged downwardly by the spring 50 and once againrotates the locking dog 34 into the groove 42 on the second locomotive24 as shown in FIG. 3. Thus, the second locomotive 24 is again connectedto the first locomotive 22 and the complete assembly can be pumped upand out of the curved tubing 14.

As previously indicated, the first locomotive 22 is normally stopped andretained in the retaining nipple 60 while the second locomotive 24 ismoved through the well tubing 12. However, the smaller locomotive 24-may become inoperative or it or its equipment may become stuck in thewell tubing 12 and require the passage of an additional locomotive 24 tobe pumped in to fish out the stuck locomotive 24. In that event it isdesired to at least temporarily remove the stationary locomotive 22 fromthe tubing 14 to perform fishing operations.

Referring now to FIG. 4, a retrieving locomotive generally indicated bythe reference numeral 81 may be provided having a body 82 and a seal 84for being pumped down into the tubing 14 so as to engage, unlock, andretrieve the first locomotive 22.

Referring to FIGS. 3 and 4, it is noted that the first locomotive 22 maybe provided with an internal recess 73 connected to the sleeve 72. Thus,the retrieving locomotive 81 may include a plurality of engaging fingers86 carried by the body 82 and urged downwardly by a spring 88 andsurrounding a wedge member 90. Thus, as the retrieving locomotive 81 ismoved downward toward the locomotive 22, the fingers 86 will contact theupper end of the sleeve 72 and move upwardly against the spring 88 andabove the wedge 92 v of the member 90 so as to cam into the recess 73 ofthe sleeve 72 on the second locomotive 22. The spring 88 will then movethe fingers 86 downward where they are wedged tightly in the recess 73.When flow in the tubing is reversed, the retrievable locomotive8l willmove upwardly pulling the sleeve 72 upwardly from beneath the latchingdogs 34 to remove the dogs 34 from the recess 64. Both locomotives 81and 22 are now free for return to the surface through the tube 14.

The method of the present invention is apparent from the description ofthe foregoing apparatus and includes the method of running subsurfacewell equipment in a well tubing through an enlarged curved tubingconnected to the upper end of the well tubing by releasably connecting afirst locomotive sized to be transported through the enlarged tubing toa second locomotive sized to be transported through the well tubing, andpumping the first locomotive through the enlarged tubing therebycarrying the second locomotive and well equipment therethrough,releasing the locomotives from each other and retaining the firstlocomotive in the enlarged tubing, and pumping the second locomotive inthe well tubing to carry the well equipment to the desired location inthe well tubing. The method further comprehends retrieving wellequipment from the well tubing after connecting the well equipment tothe second locomotive by pumping the second locomotive and wellequipment up the well tubing, connecting the second locomotive to thefirst locomotive and pumping the first locomotive up the enlarged tubingthereby carrying the second locomotive and well equipment to thesurface.

The present invention, therefore, is well adapted to carry out theobjects and attain the ends and advantages mentioned as well as othersinherent therein. While a presently preferred embodiment of theinvention is given for the purpose of disclosure, numerous changes inthe detail of construction and arrangement of parts and steps of theprocess will readily suggest themselves to those skilled in the art andwhich are en compassed within the spirit of the invention and the scopeof the appended claims.

What is claimed is:

1. In an apparatus for running and retrieving subsurface well equipmentin a well tubing by fluid flow through a curved tubing connected to theupper end of the well tubing, the improvement comprising,

said curved tubing having an inside diameter greater than the insidediameter of said well tubing, and

a retaining nipple between the curved tubing and the well tubingincluding releasable retaining means for releasably retaining a largelocomotive, but allowing the passage of a small locomotive into the welltubing.

2. The apparatus of claim 1 wherein the retaining means includes arecess.

3. The apparatus of claim 1 wherein the retaining means includes,

an upwardly directed shoulder, and

a recess below said shoulder.

4. The apparatus of claim 3 including,

a second upwardly directed shoulder below said recess.

5. An apparatus for running and retrieving subsurface well equipment ina well tubing by fluid flow through a curved tubing connected to theupper end of the well tubing, comprising,

said curved tubing having an inside diameter greater than the insidediameter of said well tubing,

a first locomotive having an outside diameter substantially equal to theinside diameter of the curved tubing for movement in the curved tubingin response to fluid,

a second locomotive having an outside diameter substantially equal tothe inside diameter of the well tubing for movement in the well tubingin response to fluid, and

releasable engaging means between the first and second locomotiveswhereby the first locomotive 8. The apparatus of claim 7 wherein theretaining nipple includes an upwardly directed shoulder and a recess forengaging and actuating the releasable engaging means between the firstand second locomotives.

9. The apparatus of claim 8 wherein the releasable engaging meansincludes,

a groove on the second locomotive,

a locking dog on the first locomotive,

yieldable means on the first locomotive normally holding the dog in thegroove but engageable with the shoulder on the retaining nipple forreleasing the second locomotive from the first locomotive.

10. The apparatus of claim 8 including,

second yieldable means on the first locomotive acting on the dog in adirection to disengage the dog from the groove and contacting saidsecond locomotive when the locomotives are engaged thereby beinginefficientive to move said dog, but actuating the dog into theretaining nipple recess when the second locomotive is released.

11. The apparatus of claim 10 including,

a shoulder on the second locomotive for engaging the second yieldablemeans when the second locomotive is moved toward the first locomotivefor releasing the first locomotive from the retaining nipple andreengaging the second locomotive with the first locomotive.

12. The apparatus of claim 5 wherein the releasable engaging meansincludes,

a groove on one of the locomotives,

a locking dog on the other locomotive, and

spring means yieldably holding the dog in the groove.

13. An apparatus for running and retrieving subsurface well equipment ina well tubing by fluid flow through an enlarged curved tubing connectedto the upper end of the well tubing comprising,

a first locomotive having an outside diameter substantially equal to theinside diameter of the enlarged curved tubing for movement in the curvedtubing in response to fluid,

a second locomotive having an outside diameter substantially equal tothe inside diameter of the well tubing for movement in the well tubingin response to fluid, and

releasable engaging means between the first and second locomotiveswhereby the first locomotive may transport the second locomotive throughthe enlarged curved tubing but allowing the smaller 6 second locomotiveto move alone in the smaller well tubing.

14. The apparatus of claim 13 wherein the first locomotive includes alongitudinal fluid passageway therethrough which is closed when thefirst and second locomotives are connected together, but is open whenthe locomotives are disconnected.

15. The apparatus of claim 13 wherein the releasable engaging meansincludes,

a groove on one of the locomotives,

a locking dog on the other locomotive, and

spring means yieldably holding the dog in the groove.

16. The apparatus of claim 13 wherein the first locomotive includes alongitudinal passageway therethrough,

a locking dog on the bottom end,

means urging said dog outwardly for engagement with the tubing, and

means urging said dog inwardly for engagement with said secondlocomotive.

17. The apparatus of claim 16 including,

said means urging said dog outwardly extending upwardly for engagementwith a releasing tool for releasing the first locomotive from thetubing.

18. An apparatus for running and retrieving subsurface well equipment ina well tubing by fluid flow through a curved tubing connected to theupper end of the well tubing comprising,

said curved tubing having an inside diameter greater than the insidediameter of said well tubing thereby allowing the passage of wellequipment of longer length,

a first locomotive having an outside diameter substantially equal to theinside diameter of the curved tubing for movement in the curved tubingin response to fluid,

a second locomotive having an outside diameter substantially equal tothe inside diameter of the well tubing for movement in the well tubingin response to fluid,

a retaining nipple between the curved tubing and the well tubingincluding an upwardly directed shoulder and a recess below said shoulderfor releasably retaining the first locomotive but allowing the passageof the second locomotive into the well tubing,

releasable engaging means between the first and second locomotivesincluding,

a groove on the second locomotive,

a locking dog on the first locomotive,

first yieldable means on the first locomotive normally holding the dogin the groove but engageable with the shoulder on the retaining nipplefor releasing the second locomotive from the first locomotive, and

second yieldable means on the first locomotive acting on the dog in adirection to disengage the dog from the groove and into the recess onthe retaining nipple.

19. The method of running subsurface well equipment in a well tubingthrough an enlarged curved tubing connected to the upper end of the welltubing, comprising,

releasably connecting a first locomotive sized to be transported throughthe enlarged tubing to a second locomotive sized to be transportedthrough the well tubing,

equipment from the well tubing after connecting the well equipment tothe second locomotive comprising,

pumping the second locomotive and the well equipment up the well tubing,connecting the second locomotive to the first locomotive, pumping thefirst locomotive up through the enlarged tubing carrying the secondlocomotive and the well equipment.

1. In an apparatus for running and retrieving subsurface well equipmentin a well tubing by fluid flow through a curved tubing connected to theupper end of the well tubing, the improvement comprising, said curvedtubing having an inside diameter greater than the inside diameter ofsaid well tubing, and a retaining nipple between the curved tubing andthe well tubing including releasable retaining means for releasablyretaining a large locomotive, but allowing the passaGe of a smalllocomotive into the well tubing.
 2. The apparatus of claim 1 wherein theretaining means includes a recess.
 3. The apparatus of claim 1 whereinthe retaining means includes, an upwardly directed shoulder, and arecess below said shoulder.
 4. The apparatus of claim 3 including, asecond upwardly directed shoulder below said recess.
 5. An apparatus forrunning and retrieving subsurface well equipment in a well tubing byfluid flow through a curved tubing connected to the upper end of thewell tubing, comprising, said curved tubing having an inside diametergreater than the inside diameter of said well tubing, a first locomotivehaving an outside diameter substantially equal to the inside diameter ofthe curved tubing for movement in the curved tubing in response tofluid, a second locomotive having an outside diameter substantiallyequal to the inside diameter of the well tubing for movement in the welltubing in response to fluid, and releasable engaging means between thefirst and second locomotives whereby the first locomotive may transportthe second locomotive through the enlarged curved tubing but allowingthe smaller second locomotive to move alone in the smaller well tubing.6. The apparatus of claim 5 wherein the first locomotive includes alongitudinal fluid passageway therethrough which is closed when thefirst and second locomotives are connected together.
 7. The apparatus ofclaim 5 including, a retaining nipple between the curved tubing and thewell tubing for releasably engaging and retaining the first locomotivefrom entering the well tubing but allowing the passage of the secondlocomotive into the well tubing.
 8. The apparatus of claim 7 wherein theretaining nipple includes an upwardly directed shoulder and a recess forengaging and actuating the releasable engaging means between the firstand second locomotives.
 9. The apparatus of claim 8 wherein thereleasable engaging means includes, a groove on the second locomotive, alocking dog on the first locomotive, yieldable means on the firstlocomotive normally holding the dog in the groove but engageable withthe shoulder on the retaining nipple for releasing the second locomotivefrom the first locomotive.
 10. The apparatus of claim 8 including,second yieldable means on the first locomotive acting on the dog in adirection to disengage the dog from the groove and contacting saidsecond locomotive when the locomotives are engaged thereby beinginefficientive to move said dog, but actuating the dog into theretaining nipple recess when the second locomotive is released.
 11. Theapparatus of claim 10 including, a shoulder on the second locomotive forengaging the second yieldable means when the second locomotive is movedtoward the first locomotive for releasing the first locomotive from theretaining nipple and reengaging the second locomotive with the firstlocomotive.
 12. The apparatus of claim 5 wherein the releasable engagingmeans includes, a groove on one of the locomotives, a locking dog on theother locomotive, and spring means yieldably holding the dog in thegroove.
 13. An apparatus for running and retrieving subsurface wellequipment in a well tubing by fluid flow through an enlarged curvedtubing connected to the upper end of the well tubing comprising, a firstlocomotive having an outside diameter substantially equal to the insidediameter of the enlarged curved tubing for movement in the curved tubingin response to fluid, a second locomotive having an outside diametersubstantially equal to the inside diameter of the well tubing formovement in the well tubing in response to fluid, and releasableengaging means between the first and second locomotives whereby thefirst locomotive may transport the second locomotive through theenlarged curved tubing but allowing the smaller second locomotive tomove alone in the smaller well tubing.
 14. The apparatus of claim 13wherein the first locomotive includes a longitudinal fluid passagewaytherethrough which is closed when the first and second locomotives areconnected together, but is open when the locomotives are disconnected.15. The apparatus of claim 13 wherein the releasable engaging meansincludes, a groove on one of the locomotives, a locking dog on the otherlocomotive, and spring means yieldably holding the dog in the groove.16. The apparatus of claim 13 wherein the first locomotive includes alongitudinal passageway therethrough, a locking dog on the bottom end,means urging said dog outwardly for engagement with the tubing, andmeans urging said dog inwardly for engagement with said secondlocomotive.
 17. The apparatus of claim 16 including, said means urgingsaid dog outwardly extending upwardly for engagement with a releasingtool for releasing the first locomotive from the tubing.
 18. Anapparatus for running and retrieving subsurface well equipment in a welltubing by fluid flow through a curved tubing connected to the upper endof the well tubing comprising, said curved tubing having an insidediameter greater than the inside diameter of said well tubing therebyallowing the passage of well equipment of longer length, a firstlocomotive having an outside diameter substantially equal to the insidediameter of the curved tubing for movement in the curved tubing inresponse to fluid, a second locomotive having an outside diametersubstantially equal to the inside diameter of the well tubing formovement in the well tubing in response to fluid, a retaining nipplebetween the curved tubing and the well tubing including an upwardlydirected shoulder and a recess below said shoulder for releasablyretaining the first locomotive but allowing the passage of the secondlocomotive into the well tubing, releasable engaging means between thefirst and second locomotives including, a groove on the secondlocomotive, a locking dog on the first locomotive, first yieldable meanson the first locomotive normally holding the dog in the groove butengageable with the shoulder on the retaining nipple for releasing thesecond locomotive from the first locomotive, and second yieldable meanson the first locomotive acting on the dog in a direction to disengagethe dog from the groove and into the recess on the retaining nipple. 19.The method of running subsurface well equipment in a well tubing throughan enlarged curved tubing connected to the upper end of the well tubing,comprising, releasably connecting a first locomotive sized to betransported through the enlarged tubing to a second locomotive sized tobe transported through the well tubing, pumping the first locomotivethrough the enlarged tubing carrying the second locomotive and wellequipment therethrough, releasing the locomotives from each other,retaining the first locomotive adjacent the junction between theenlarged tubing and the well tubing, and pumping the second locomotivein the well tubing thereby carrying the well equipment to the desiredlocation in the well tubing.
 20. The method of claim 19 includingretrieving well equipment from the well tubing after connecting the wellequipment to the second locomotive comprising, pumping the secondlocomotive and the well equipment up the well tubing, connecting thesecond locomotive to the first locomotive, pumping the first locomotiveup through the enlarged tubing carrying the second locomotive and thewell equipment.